Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/17/2007
Publication Date: 5/18/2007
Citation: Ye, L., Tuo, W., Liu, X., Zhu, X. 2007. Identification and characterization of a novel splicing variant of the MHC classI-related Neonatal Fc receptor for IgG. Meeting Abstract. Interpretive Summary: The IgG receptor FcRn is important to transport maternal IgG to fetuses and newborns and to preserve IgG in adults. The present study discovered a new porcine IgG receptor, pFcRn-S. The protein sequence of the pFcRn-S is shorter than the full length pFcRn, but it is fully functional in binding IgG. It also differs from the full length pFcRn in that the subcellular destination for pFcRn is lysosome and the trafficking to this compartment is independent of beta 2-microbulin. Continued research in pFcRn and its variants will facilitate our understanding of IgG transport and protection throughout life time of livestock animals.
Technical Abstract: The neonatal Fc receptor for IgG (FcRn), a MHC class I-related molecule, functions to transport maternal IgG into the fetus or newborn via placenta and/or intestine and protects IgG from catabolism. The mRNAs of several MHC class I-related molecules have multiple splicing variants. In the course of cloning porcine FcRn cDNA from the intestinal epithelial cell line IPEC, two cDNAs were found: a long form of 1.2-kb (pFcRn-L) and a short form of 0.75 kb (pFcRn-S). These mRNAs were also detected in porcine kidney epithelial cell line LLC-PK1, peripheral blood mononuclear cells, as well as a variety of porcine tissues by RT-PCR and Northern blot. Sequence analysis showed that pFcRn-L cDNA encodes the full-length pFcRn, whereas pFcRn-S cDNA represented a splicing variant of pFcRn mRNA, coding for a truncated pFcRn with deletion of 92 amino acids matching to the alpha2 domain of pFcRn-L. Recombinant pFcRn-L bound IgG at pH 6.0, but not at pH7.5. However, recombiunant pFcRn-S bound IgG at both pH 5.0-6.0 and pH 7.5. Furthermore, the intracellular trafficking patterns of pFcRn-L and pFcRn-S exhibited remarkable differences. The pFcRn-L was expressed on the cell surface and mainly localized in the early endosomal compartment, whereas pFcRn-S was primarily found in late endosome/lysosome. In contrast to pFcRn-L, pFcRn-S trafficking to the lysosomal compartment is independent of porcine beta2m expression as assessed in a beta2m-deficient cell line FO-1. This suggests that pFcRn-S may have an alternate function in lysosomal compartment. Therefore, the pattern of FcRn gene expression which is characterized by the complexity of RNA splicing further implies the functional complication of the FcRn receptors.